Production of artificial yarns



Feb. 17, 1942. w. w. HECKERT PRODUCTION OF ARTIFICIAL YARNS Filed NOV. 15, 1939 ATTORNEY Patented Feb. 17, 1942 PRODUCTION OF ARTIFICIAL YARNS Winfield Walter Heckert, Wilmington, Del., as-

signor to E. I. du Pont de Nemours a Company, Wilmington, DeL, a corporation of Delaware Application November 15, 1939, Serial No. 304,495

4 Claims.

This invention relates to improvements in the preparation of yarn from artificial filament-forming materials.

Heretofore, difiiculties have been encountered in all of the conventional spinning methods in producing filaments and yarn of uniform denier because of pulsations in the flow of the filamentforming material through the spinneret. It is to be understood that in referring to denier of filaments or yarn, I do not use the term in the customary sense, as based on. the mass (in grams) of 9000 meters as determined on long sections of yarn. I am rather referring to the denier as it is calculated from measurements of the mass of comparatively short lengths of filaments or yarn (e. g., 9 centimeters or less); for the denier deviations to which I refer are manifested only in very short lengths of the filaments or yarn; These deviations, though varying in magnitude, are repeated more or less periodically and, in a long section of filaments or yarn, are not shown to an. appreciable extent in denier values determined by the conventional methods.

Non-uniformities of denier may be due to irregularities incident to the pumping of the filament-forming material to the extrusion nozzle, but may be due also to other conditions. Gas bubbles in a filament-forming composition, particularly in a molten filament-forming composition, may cause such denier variations. This is particularly true of synthetic linear polyamides, which are melt spun, because they decompose somewhat when held at temperatures above their melting points. Also, drafts of air around the spinneret face or around the bundle of filaments emerging from the spinneret may cause denier irregularities. Such drafts may cause certain filaments to freeze more quickly than others, thus causing variations in the points of freezing of the various filaments with respect to the distance from the spinneret face. A very small amount of wandering of the freezing point may cause marked variations in denier. Small variations in air flow will cause independent variation in filament deniers, whereas a strong draft or gust will cause the filament deniers to vary in unison, that is, at the same point in the bundle.

As a result of these irregularities, the filae merits vary in size from point to point along each filament and, unfortunately, when a large number of the filaments, or even all of the filaments, vary in size at the same point in the yarn bundle, these irregularities in filament size are multiplied in the yarn. If more material is pumped than usual, each filament assumes a 55 greater than usual size: or, in other words, a nub (or enlargement) is introduced upon each filament at the same point in the yarn bundle such that, when the filaments are brought together as a yarn, a large nub on the yarn results. If less material is pumped than usual, each filament assumes a smaller than usual size at the same point in the yarn bundle, thus imparting to the resulting yarn a decidedly smaller denier at certain points in contrast to the normal denier,

and the denier at the points where nubs have been formed. In other words, the yarn obtained by spinning with the standard types of spinneret assemblies and pumps has larger cross-sections neret face very much without encountering many other difficulties. Also, tipping the spinneret face may enhance the difiiculties of controlling the point of freezing, and tipping does not correct variations in denier caused by bubbles in the melt, by drafts, by variations in wind-up speed, a

or by variations in the traversing stroke.

This matter of non-uniformity of denier of yarn is of particularly great concern in thepreparation of filaments and yarns from melts of polyamides and other filament-forming linear polymers, for these yarns are usually drawn after the spinning operation; and non-uniformities of yarn denier, such as I have described above, markedly affect the drawability of the yarn, the tenacity of the yarn, and the resultant dye aflinity of the drawn yarn. It is well known that Y slight differences in the extent of drawing of polyamide yarns will cause distinct differences in shade in the dyed yarn or fabric and will, in, many cases, cause one part of the yarn or fabric to exhibit an entirely different color from that exhibited by another part of the yarn or fabric. This is a very serious matter; for the value of both yams and fabrics depends in large measure on a predetermined uniformity of color and shade.

No satisfactory method has heretofore been developed for controlling these non-uniformities illustration when taken in connection with the following detailed description. The figure is a diagrammatic side elevational view of the apparatus constructed in accordance with the invention.

Referring to the illustration, the filamentforming material Ill, melted or in solution, is fed by a suitable pump or metering device 9 to a spinneret assembly 4. The filament-forming material is forced through spinneret 5, from which it is extruded as a plurality of filaments 6 with periodic nubs I (greatly enlarged). These filaments 6 pass through a convergence guide 8 to positively driven feed roll I, pass under feed roll I, are separated into two bundles of filaments I3 and I4, each of which passes over a difierent positively driven feed roll (filament bundle I4 passing over feed roll 2, filament bundle I3 passing over feed roll 3), are reunited at convergence guide I6 to form yarn I5, and as such are wound on bobbin II as yarn cake I2.

As filament bundle 6 leaves feed roll I, the nubs I are in the same relative positions asshown by Ia and lb. However, due to the longer path taken by nubs lb, the nubs ID are thrown out of phase with respect to nubs Ia, as shown by the relative positions Ia and 1b. seen that the nubs I of the filaments 6, starting out from spinneret 5 at the same instant would not end in the same relative position with respect to one another in yarn I5 if the size and revolutions per minute of feed rolls 2 and 3 are equal and the thread speed of filament bundles I3 and I4 is equal, since filament bundle I4 travels through a longer path than filament bundle l3 and thus will be thrown out of phase with filament bundle I3. The distance out of phase will be the difference in length of path traveled by the two separate bundles of filaments. The resulting yarn I5 will have the filament sectionsof larger and smaller cross-sections; distributed in a different relation from the distribution that occurs when all of the filaments travel through the same length of path from the spinneret to the wind-up device. In general, this different distribution of the larger and smaller filament crosssections serves to produce a yarn of more uniform denier.

It is to be noted that the important factor determining the distribution of the larger filament cross-sections and the smaller filament cross-sections in the resulting yarn is the distance out of phase of the various: filament bundles; in other words, the difference in length of path traveled by the different filaments in passing from spirmeret to wind-up device.

The following detailed examples are submitted to illustrate the invention. It is to be understood, however, that the invention is not limited to the specific details set forth in these examples.

Thus it is Example I Polyhexamethylene adipamide, maintained melted at 285 C., is fed by a gear pump to a spinneret (containing 20 holes). The filaments emerging from the spinneret pass through a convergence guide (such as 8 in the drawing) to a positively driven feed roll, such as feed roll I in the drawing, then in two separate bundles over feed rolls, such as feed roll 2 and feed roll 3 in the drawing, of equal size and speed, then together again to form a yarn such as yarn I5 in the drawing. The feed rolls 2 and 3 are so positioned that one bundle of filaments travels 2% meters farther than the other between the point of separation on feed roll I and the point of convergence at convergence guide I6. The resulting yarn has the nubs in the several filaments distributed more or less uniformly along its length as is shown by the fact that a number of series of Q-centimeter denier measurements indicate a coefiicient of variation of 1.38 and that the average of the spreads is 5.4% of the denier.

A control experiment is run with materials and conditions the same as in Example I, with the exception that the filaments are not out of phase, but rather travel in a single bundle from spinneret to wind-up bobbin. The coefllcient of denier variation is 4.46 and the average spread is 10.5% of the denier, both values being much higher than in the above example in which the filaments are out of phase.

' Example 11 Polyhexamethylene sebacamide is spun into open air to give 1'70-denier, IO-filament yarn using a spinneret with 10 orifices located on a circle of an inch in diameter. Under these conditions, random air currents in the room cause random denier variations, but the filaments being located so close together are affected at substantially the same time. Consequently, their deniers vary substantially in unison. The 10 filaments are separated after passing around the feed roll I and each filament is passed over an individual guide taking the place of the feed rolls 2 and 3 in the drawing. These guides are so arranged that one filament travels around one guide along one path, a second filament travels around another guide along a path about 27 centimeters longer than that of the first-named filament, a third filament travels around a third guide along a path about 27 centimeters longer than that of the second filament, a fourth filament travels around a fourth guide along a path about 27 centimeters longer than that of the third filament, etc. In this manner yarn is spun having a coefiicient of 9-centimeter denier variation of about 1.9. If the filaments all travel the same path. the coefiicient of denier variation is found to be about 5.

The coefficient of variation, as used above, is

defined by the following formula:

where O- is the root means square of the deviations from the average denier X.

In case one desires to reduce denier variations which occur in a random manner with respect to the yarn as a whole as in Example II, particularly good results are obtained when paths taken by different portions of the filament bundle differ by a small multiple of the length of yarn which when used in denier measurements yields the largest coefficient of variation. For

example, in Example II, S-centimeter measurements yield a coeflicient of variation of for the control yarn, whereas 9-meter measurements yield a coefficient of variation of about 2. A small multiple of the Q-centimeter measurement, namely 27 centimeters, was chosen as the ina l t oo v V to throw the filaments out of phase. Moreover,

crement by which to vary the length of the path. I

Nine meters could also be used, but would be unnecessary and the equipment required would prove to be very awkward to handle. In the case of periodic denier variations the increment by which the path is increased can be chosen by spinning of .polyhexamethylene adipamide and' polyhexamethylene sebacamide, synthetic linear polyamides. However, the invention is not limited to these filament-forming materials, but is applicable to the spinning of any filament-forming material from melt or from solution.

The filament-forming material used in accordance with the present invention may contain modifying agents; e. g., luster-modifying agents, plasticizers, pigments and dyes, antioxi dants, resins, etc.

The means for pumping or metering the filament-forming material may comprise gear pumps, screw pumps, piston pumps, or'in fact, any other type of means for forcing the filament forming material through the spinneret assembly, including the application of high gas pressures using gases which are preferably inert to the filament-forming materials and of limited solubility in them; e. g., oxygen-free nitrogen or hydrogen.

It is to be understood that this invention capable of correcting denier variations arising from any source related to the spinning process, such as bubbles, drafts, variation of wind-up speed, variation of traversing stroke, etc., as well as pumping variations; but the invention is particularly useful in correctingdenier variations caused by bubbles in the melt or by drafts of air passing across the filaments as they emerge from the spinneret.

While the feed rolls described in theabove stantially the same diameter and are rotated at -vention have been found to make possible the substantially the same rate, it is to be clearly sible the movement of two or more bundles of filaments or a plurality of individual filaments, through a plurality of paths, such that the filaments are thrown out of phase in the resulting yarn; lies within the scope of this invention. It is also to be understood that the use of any other means, such as snubbing pins, thread guides, etc., for separating the filaments into two or more bundles or into individual filaments, conducting the filaments through paths of different lengths and reuniting the filaments out of phase in a yarn, lies within the scope of this invention.

Although I have specifically disclosed paths differing by 2.5 meters and by 27 centimeters to 270 centimeters, it is to be clearly understood that these are merely illustrative. Knowing the periodicity of the variations of the denier of the yarn, it is well within the province of a skilled worker to calculate the length of path required the filaments can be thrown just out of'phase (say 1 centimeter) or they can be thrown out of phase so the nubs of the filaments are uniformly distributed along the length of yarn, and this, of course, is optimum.

The invention is not limited to the specific spinneret assembly or any part thereof or to the specific convergence guide or to the specific windup device described above. The use of any conventional means for accomplishing the functions of these parts, when used in accordance with this invention, lies within its scope.

While the invention has been described particularly with regard to the attainment of uniform dyeing characteristics, it is obvious that it is of great value for obtaining improvements in the uniformity of properties other than dye affinity.

Y The method and apparatus of the present ingreatest difiiculties caused by the pulsations in the flow of filament-forming material from pump to spinneret, to average the non-uniformities of denier caused by these pulsations or by other varying conditions by throwing the filaments out of phase, thus producing yam of much greater uniformity as to denier, tenacity, drawability and dye afflnity than have heretofore been possible. This invention makes possible the production of fabrics of'great uniformity of dye aflinity. It makes possible the production of stockings free .from the troublesome rings and ladder marks which formerly resulted from inequalities of dye affinity. It makes possible the production of extremely sheer fabrics of various types free from the undesirable differences in shade and in color which formerly were obtained because of even very slight non-uniformities of denier. This invention makes possible the production of pile fabrics of excellent quality by reason of its elimination of the non-uniformities of denier which so frequently cause the formation of so-called shiners or neps" in pile fabrics. It is to be especially noted that this invention makes possible the production, from polyhexamethylene adipamide, of yarn of exceptionally great uniformity as to denier, 'drawability, and dye affinity and that such yarn may be converted into fabrics of a wide variety of types which possess exceptionally great uniformity of color and shade of color, of hand, drape, flexibility, and other characteristics. It is to be' clearly understood, however, that the application of this invention to polyhexamethylene adipamide is only illustrative and that the invention is not so limited. The invention may be used to great advantage in preparing filaments, yarn, and fabrics of great uniformity from a large number and wide variety of other filament-forming materials.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not-to be limited except as set forth in the appended claims.

I claim:

1. Apparatus for diminishing yarn denier differences in the production of artificial yarn from filament-forming material which comprises a spinning nozzle for producing a plurality of filaments, guide means about which all of said filaments are passed to draw the same at equal speeds from said nozzle, a filament converging means, a second guide means positioned to guide at least one of said filaments from said firstnamed guide means to said filament converging means, a third guide means positioned to guide at least one other of said filaments from said first-named guide means to said filament converging means, said second guide means and said third guide means being so positioned that the distance from the first-named guide means about said second guide means to the convergence means is materially different from the distance from the first-named guide means about said third guide means to the convergence means.

2. The apparatus defined in claim 1 in which said guide means for causing said plurality of filaments to travel over paths of different length, comprises rollers rotating at substantially the same peripheral speed.

3. The apparatus defined in claim 1 in which said means for causing said plurality of filaments to travel over paths of different length, comprises positively driven rollers rotating at substantially the same peripheral speed.

4. A method of diminishing denier difierences of continuous filament yarn which comprises separating a bundle of freshly spun filaments as they pass from a spinneret to a collecting device 

